Substance P protects spiral ganglion neurons from apoptosis via PKC-Ca2+-MAPK/ ERK pathways.
In the current study, we have investigated the ability of substance P ( SP) to protect 3-day-old (P3) rat spiral ganglion neurons (SGNs) from trophic factor deprivation (TFD)-induced cell death. The presence of SP high affinity neurokinin-1 receptor (NK1) transcripts was detected in the spiral ganglion and the NK1 protein localized to SGNs both ex vivo and in vitro. Treatment with SP increased cytoplasmic Ca2+ in SGNs, further arguing for the presence of functional NK1 on these neurons. Both SP and the agonist [Sar9,Met(O2)11]-SP significantly decreased SGN cell death induced by TFD, with no effect on neurite outgrowth. The survival promoting effect of SP was blocked by the NK1 antagonist, WIN51708. Both pan-caspase inhibitor BOC-D-FMK and SP treatments markedly reduced activation of caspases and DNA fragmentation in trophic factor deprived-neurons. The neuroprotective action of SP was antagonised by specific inhibitors of second messengers, including 1.2-bis-(O-aminophenoxy)-ethane-N,N,N',N'-tetraacetic acid (BAPTA-AM) to chelate cytosolic Ca2+, the protein kinase C ( PKC) inhibitors bisindolylmaleimide I, Gö6976 and LY333531 and the MAPK/ ERK inhibitor U0126. In contrast, nifedipine, a specific inhibitor of l-type Ca2+ channel, and LY294002, a phosphatidylinositol-3-OH kinase ( PI3K) inhibitor, had no effect on SP trophic support of SGNs. Moreover, activation of endogenous PKC by 4 beta-phorbol 12-myristate 13-acetate (PMA) also reduced the loss of trophic factor-deprived SGNs. Thus, NK1 expressed by SGNs transmit a survival-promoting regulatory signal during TFD-induced SGN cell death via pathways involving PKC activation, Ca2+ signalling and MAPK/ ERK activation, which can be accounted for by an inhibition of caspase activation.[1]References
- Substance P protects spiral ganglion neurons from apoptosis via PKC-Ca2+-MAPK/ERK pathways. Lallemend, F., Lefebvre, P.P., Hans, G., Rigo, J.M., Van de Water, T.R., Moonen, G., Malgrange, B. J. Neurochem. (2003) [Pubmed]
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